Magnetic induction technology is based on the quasi-static magnetic component of the field generated by a coil through which a sinusoidal current is flowing. When a second coil is introduced within that field, the magnetic flux passing through that second coil induces a modulated current in it. This phenomenon has been used for communication between a magnetic induction transmitter and magnetic induction receiver using near-field propagation where the magnetic field is much greater than the electric field and is inversely proportional to the cube of the distance from the transmitting coil. The coils are tuned to resonate at a desired frequency by employing programmable capacitance. The coils may be mounted on a ferrite core to increase the transmission efficiency. Typical operating parameters for a magnetic induction communication system, such as may be employed for an ultra low power hearing aid, are a carrier frequency of 10.579 MHz and a modulation rate of 298 kbits−1 using FSK modulation at a modulation index of 1.0 and having a bandwidth of about 600 kHz. A receiver in such a low power communication system has a sleep mode in which power is conserved by powering-up the receiver only intermittently to monitor for a received signal, and maintaining the receiver powered-up to synchronise only if a signal is present.
An object of the invention is to enable improved power conservation in a wireless receiver.